My research associates, postdoctoral fellows, and graduate students and I conduct research along two principal lines: 1) photoreceptors and 2) cytodifferentiation. Under the former we shall continue to sample photoreceptors in animal phyla not yet examined (e.g., Nematomorpha, Nemertinea), further our efforts to determine the effects of light and darkness upon the ultrastructure of light sensitive cells particularly those in the snail Helix aspersa), continue our investigation of the function of the unique 800 A vesicles in the photoreceptoral cells of mulluscan eyes, study regeneration of ocelli in seastars, analyze the sensitivity of different strata in the retina of a jumping spider to different wave-lengths of light, and study the effects of vitamin A deficiency on the receptoral cells in the eyes of H. aspersa. The chief trust in embryology, principally by my graduate students, will be in the area of early ultrastructural differentiation in the neural tube of amphibian embryos with particular attention to cell death in amphibian neurogenesis, the role of microfilaments in the embryonic differentiation of the thyroid gland of chicks, etc.